1. Field of the Invention
The present invention relates to a wheel structure and a wheel mounting method in a motorcycle.
2. Description of Background Art
A wheel structure for a rear wheel for a motorcycle is known wherein a driven sprocket and a hub are disposed in a relatively rotatable manner with a wheel damper disposed between the driven sprocket and the hub to prevent propagation of a shock from the driven sprocket side to the hub side as disclosed in Japanese Patent Publication No. Hei 8-25363, pages 2 and 3, FIG. 3.
FIG. 3 in Japanese Patent Publication No. Hei 8-25363 will now be described with reference to FIG. 26 attached to the present application, in which reference numerals have been newly assigned. FIG. 26 is a sectional view showing a conventional wheel structure.
According to this conventional wheel structure, a collar 402 is fitted on an axle 401. A hub 407 of a rear wheel 406 is secured to the collar 402 rotatably through bearings 403 and 404 with a cover 408 attached to one end portion of the hub 407 with a bolt 411. A driven sprocket 413 is connected to the cover 408 through a buffer mechanism 412. A base portion 415 of a large diameter is formed centrally of the collar 402. Extending portions 416 and 417 are provided that are of a small diameter and are formed on both sides of the base portion 415 of the collar 402. A rear fork 418 is provided for supporting both ends of the axle 401.
Now, with reference to FIG. 27, a description will be given below of a method for mounting the rear wheel constructed as above.
FIG. 27 is an operation diagram showing a conventional wheel mounting method for mounting the rear wheel. The first the hub 407 and the cover 408 are connected together with bolt 411. One bearing 404 is press-fitted into a bearing hole 421 formed in the cover 408. The extending portion 417 of the collar 402 is fitted through the bearing 404.
As indicated by the arrows, the other bearing 403 is press-fitted into a bearing hole 422 formed in an end portion of the hub 407 with an inner surface of the bearing 403 being fitted on the extending portion 416 of the collar 402.
In FIG. 27, a predetermined press-fit load is needed for press-fitting the bearing 403 into the bearing hole 422. This load is imposed on the other bearing 403 through the collar 402. If the press-fit load on the bearing 403 is equal to that on the bearing 404, it becomes difficult for the bearing 404 to bear the press-fit load when the bearing 403 is press-fitted into the bearing hole 422. Therefore it has been desired to take a special measure for bearing the press-fit load.
The hub 407 is required not only to have rigidity against the press-fit load on the bearing 403 but also to be rigid enough against a load imposed thereon during vehicular operation.
For enhancing the rigidity of the hub 407, it may be effective to adopt, for example, a method of increasing the wall thickness of the hub 407. According to this method, however, it is necessary to change the shape of a die used, which is not easy. In addition, a large increase in the cost results.